Recent development of networking has created new applications for network communication devices for communication over the Internet or like network.
For instance, there are scanner communication devices which can transmit image information read from a document to an external device (e.g. a computer) connected to a network.
As an example of such scanner communication devices, a device having “Scan to Email” function has been developed.
This device converts the image information read from a document to data with a particular format so as to generate an attachment file for e-mail, and transmits an e-mail message including the attachment file to a designated destination (e.g. a host computer) on the Internet.
Also, network facsimile machines (Internet facsimile machines) having printing and telephone functions in addition to the scanner communication function have been developed.
This Internet facsimile machine generates and transmits an e-mail message including an attachment file with image information having been read, and as a received document, the Internet facsimile machine prints (records and outputs) an attachment file of a received e-mail message on a sheet.
Document (1) (Japanese Laid-Open Patent Application No. 2001-274944 (Tokukai 2001-274944; published on Oct. 5, 2001)) discloses a communication system (Internet facsimile system) including such an Internet facsimile machine.
FIG. 38 is a schematic block diagram showing this system. In the Internet facsimile system, when an e-mail message (including an attachment file) is transmitted from an Internet facsimile machine 101 to an Internet facsimile machine 105, first, the Internet facsimile machine 101 transmits (posts) the e-mail massage to a mail server 102 of the Internet facsimile machine 101 itself.
Then the e-mail message posted to the mail server 102 is transferred to a mail server 104 of the Internet facsimile machine 105 via a network 103 and stored in the mail server 104, under a predetermined e-mail transfer protocol such as SMTP (Simple Mail Transfer Protocol).
The Internet facsimile machine 105 regularly accesses the mail server 104, and obtains stored e-mail messages. To obtain the e-mail messages, mail receiving protocols such as a POP3 (Post Office Protocol Version 3) protocol and an IMAP (Internet Message Access Protocol) are used.
Further, the Internet facsimile machine 105 receives an e-mail message and prints the attachment file (image information) thereof, as a received document, and then, in order not to redundantly carry out the reception of the message, typically instructs the mail server 104 to delete the received e-mail message.
However, this Internet facsimile system has the following inherent problem which is not observed in a typical facsimile communication.
That is to say, since a typical facsimile communication realizes a bi-directional real-time communication using a PSTN (Public Switched Telephone Network), a receiving end can easily transmit a reception result notification to a transmitting end, right after the reception of image data.
On the contrary, the transmission of e-mail messages by the Internet facsimile system is a one-way communication from the Internet facsimile machine 101 to the Internet facsimile machine 105, via a server (even if the Internet facsimile machine 105 is in the state of not being able to receive e-mail messages, the transmission from the Internet facsimile machine 101 to the mail servers 102 and 104 is completed anyway).
Thus, to transmit a reception result notification in the Internet facsimile system, the Internet facsimile machine 105 must generate an e-mail message (reception result mail) as a reception result notification and transmit the same to the Internet facsimile machine 101. However, the conventional arrangement does not support such a function of easily generating and transmitting a reception result mail.
For this reason, in the above-mentioned Internet facsimile system, the Internet facsimile machine 101 cannot recognize whether or not the Internet facsimile machine 105 has correctly received an e-mail message, and whether or not image information has properly been printed.
On this account, to confirm the reception of an e-mail message, telephone communication between the users of the Internet facsimile machines 101 and 105 is required after all, and this causes e-mail communication to lose one of its advantages over telephone communication that the parties involved do not need to talk with each other in real time.
To overcome this problem, a scheme is defined by the MDN (Message Disposition Notification) in RFC 2298 which allows an Internet facsimile machine received an e-mail massage to notify a reception result to a transmitting end (i.e. a method of confirming a reception result).
In this method, an Internet facsimile machine of a receiving end notifies a reception result/progress to a transmitting end, using a reception result mail with a predetermined format.
It is noted that “RFCs” (Requests For Comments) are official documents issued by IETF (Internet Engineering Task Force), an Internet-related technology standards organization.
The documents define, for example, specifications and requirements of Internet protocols, such as IP (Internet Protocol), TCP (Transmission Control Protocol), HTTP (HyperText Transfer Protocol), and FTP (File Transfer Protocol), and various Internet-related technologies. They are numbered throughout like “RFC 2298” and publicly available.
According to the MDN defined in the RFC, when the transmission of a reception result mail is desired, an Internet facsimile machine of a transmitting end adds a request (reception result request) for reception result mail to an e-mail message to be transmitted.
The request is added to a “Disposition-Notification-To:” field (MDN field) in a header of the e-mail message.
That is, the Internet facsimile machine of the transmitting end posts an address (usually an address of the device itself) to an MDN field of the e-mail message, in order to set a reception result request. Then the Internet facsimile machine received this e-mail message returns a reception result mail to the address specified in the MDN field.
Note that, such transmission and reception of a reception result mail can be carried out only when the Internet facsimile machines of the transmitting and receiving ends meet the requirement of the MDN (i.e. support the MDN function).
Technology regarding an Internet facsimile machine supporting the MDN function is, for instance, disclosed by Document (2) (Japanese Laid-Open Patent Application No. 2001-309109 (Tokukai 2001-309109; published on Nov. 2, 2001)).
According to this document, after transmitting an e-mail message including a reception result request, an Internet facsimile machine prints out an “unreceived” report, if a reception result mail is not transmitted thereto within a predetermined period of time. With this “unreceived” report, the user of the Internet facsimile machine is notified that the reception result mail is not transmitted from the transmitting end (i.e. the user is notified the occurrence of an error of e-mail transmission (due to the trouble of the communication line)).
With this arrangement, this Internet facsimile machine enables the user to easily recognize whether or not an e-mail message is properly received by a receiving end.
However, in this conventional Internet facsimile machine, when a transmission error or reception error (errors indicating that an e-mail message cannot be properly processed due to the receiving-end machine) occurs for any reason, the e-mail message is not retransmitted in order to prevent the continuous occurrence of errors.
For this reason, the conventional Internet facsimile machine cannot complete the transmission if an error occurs, and this deteriorates the efficiency of the data transmission.